When I first went to live in Buenos Aires in 2008, the biggest impression of my first lessons was the emphasis on relaxation. For some reason I had been taught to dance tango with straight legs and did not have the relaxation in my knees and hip to be able to absorb movement.
Relaxation is essential in tango for exactly this reason -to create a smooth dance, all the articulations of the hip and knee need to be able to absorb impact of the movement. If the joints and legs are stiff, dancing looks stiff and rigid, and the possibilities for movement is much more limited. Having relaxed articulations is just one piece in the tango puzzle. Being able to put this together with the right amount of tone in the muscles to dance fluidly is another piece.
What exactly does it mean to have relaxion in the hip?
Is means that your glutteal (bottom) muscles are relaxed - not pinched inward and downward like in some other dances.
It means that you have a sense that your 'sitting bones" are facing downward towards the floor - not inward or flaring outward
It means that you have a sense that your articulation of the upper part of your leg that joins with the hip is free and flexible.
What exactly does it mean to 'relax your knees'?
In Spanish the word used for how your knees should be is 'disponible". The English translation is 'available" but it doesn't make much sense in English unless you ask" Why should my knee be available?". Your knee should be 'available' to morph into whatever step you are dancing. Your knees need to be relaxed so that they can be receptive or to be channeling energy smoothly. This does not mean that your knees should be 'bent'. They should be 'soft' and never completely straight.